Electric resistance.



1, U $5 CROSS FFZAQflENtE-Z No. 756,119. PATENTED MAR. 29, 1904.

H. VON KRAMER.

ELECTRIC RESISTANCE urmouxon' FILED SEPT. 1, 1903.

H0 IODEL.

UNITED STATES Patented March 29, 1904.

HANS VON KRAMER, OF BATH, ENGLAND.

ELECTRIC RESISTANCE.

SPECIFICATION forming part of Letters Patent No. 756,119, dated March 29,1904. Application filed September I 1903- Serial No. 171,505. (No model.)

To all whom it may concern:

Be it known that I, Hans von KRAMER, a

My said invention relates to electrlc resistances of the type usually made up from an artificial-stone-like composition consisting of mixtures of non-conducting and conducting bodies, and has for its object to improve the construction of such resistances, so as to render the same efficient and durable when in use.

An electric resistance as made according to my invention is shown in sectional elevation in the accompanying drawing.

In carrying out my invention I form the body A of the resistance-piece from the composition hereinbefore referred to, but having-a smallcentral core B, of sand, clay, or equivalent material, running through it for a purpose to be hereinafter referred to.

The proportions of the materials used to form the body A will vary greatly, according to the quality of the materials and the particular purpose for which the resistance is to be used; but according to one example, especially intended for-use where low ohmic resistance is desired, about fifty per cent. of clay and forty per cent. of an equal mixture consisting of plumbago and carbon-powder is used, the whole being mixed with about ten per cent. of water-glass (silicate of soda) or alum-powder to bind the materials together.

The materials forming'the body A in a slightly-damp state are first lightly compressed within a tube. During the compression a wire occupies the central space afterward filled up by the sand core B. One end of the contact-pole C for each end of the resistance-piece is embedded in a carbon plug D of high conductivity, (for example, of ordinary arc lamp carbon,) which projects into a layer E of a carbon mixture of high conductivity, the carbon being mixed with only and suflicient clay and water-glass or alum to bind the particles together. This plug D and layer of carbon E are embedded in the resistance material A in the tube. The wire is then withdrawn, the sand core B filled in, and the contact-poles C inserted into the carbon plugs, or the poles may not be placed in position until the resistance is completed. The layers of highly-conductive material are curved on their inner faces, as shown, in

order that the total resistances at any points.

in its section from pole to pole of the resistance-piece may be equal-that is to say, the

length of resistance material A traversed by current at its outer parts is just so much less as to make the total resistance of those parts, together with the resistance of the greater amount of highly-conductive layer the current has then to pass through, exactly equal to the total resistance of the longer central.

parts, together-with the smaller amount of highly-conductive layer the current has in the latter case to pass through, and this produces conductive terminals of great efliciency, as the current is spread by them throughout ,the whole areaof the resistance without tending to pass through (and unduly heat) the central parts, avoiding the outer parts, as would be the case if the conducting layers E were flat. The tube, with its contents, is placed in a mold slightly larger than the tube, and the space between the tube and the mold is filled with a non-conducting and refractory material G, a layer of this material being also placed in the mold, so as to cover the carbon layers E and plugs D. position before the tube is inserted in the mold given as an example: sixty per cent. clay,.

twenty per cent. brick-dust, with about twelve per cent. of binding materials and eight per- The bottom layer is placed in I the top layer after the tube has been withdrawn. This non-conducting mantle G con-' cent. of lubricant. After the tube is withdrawn the contents of the mold are subjected to by draulic pressure (preferably applied by a plunger entering the mold) in order to give the finished resistance the required density. During this action any air in the materials finds its way to'and is absorbed by the central core B, of sand or the like, with the result that the homogeneity of the mass is in-' sured. At the same time the materials forming the mantle G, the body A, the carbon layers E, and plugs D, while merging into each other at the point ,of contact, are distinct-that is to say, there is a distinct layer of non-conducting material on the outside. The resistance-piece so formed is heated at a comparatively high temperaturesay 600 F ahrenheit-until it becomes thoroughly hard, which heating period may occupy three to five days.

In order to further improve the insulation and also to keep out air, a sheet of mica His wound, preferably helically, on the resistancepiece, and the ends are covered and the mica held in place by insulating-caps J. These caps are preferably made of a composition of seventy-five per cent. firebrick dust, with twenty-five per cent. water-glass, put on in a soft state and fused in position.

. The contact-poles (J are of such a length that they project through the caps J, and they may be fitted with any known forms of binding screws and nuts.

When current is allowed to pass to one of the contact-poles C, it is collected by the plug 1) and the layer E, of carbon, at that end, and

- it passes inconsequence of the special form of the layer E in equal current lengths through the body A of the resistance-piece to the other contact-pole.

What I claim-as my invention is r 1. An electric resistance comprising a body 2 core of sand therein, a mantle of non-conduct formed of a mixture of conducting and nonconducting and binding mater als, a central r and binding materials surrounding the and conducting-terminals embedded in the body, as described.

2. Ah electric resistance comprising a body formed of a mixture of conducting and nonconducting and binding materials, a central core of sand therein, a mantle of non-conducting and binding materials surrounding the body layers of highly-conductive material internally concave at the ends of the body, and terminals embedded in such layers, as described.

3. An electric resistance comprising a body formed of a mixture of conducting and nonconducting and binding materials, a central coreof sand therein, a mantle of non-conducting and binding materials surrounding the body, layers of highly-conductive material internally concave at the ends of the body, carbon plugs in the layers and contact-poles embedded in the carbon plugs, as described.

4. An electric resistance comprising a body formed of a mixture of conducting .and nonconducting and binding materials, a central core of sand therein, a mantle of non-conducting and binding materials surrounding the body, terminals of highly-conductive material at the ends of the body, sheet-,mica surrounding the mantle, and insulating-caps of non-conductive and binding materials covering the ends and holding the mica in place, as described.

In testimony whereofl have signed my name to this specification in the presence of two subscribing witnesses.

VON KRAMER.

WVitnesse's: DAVID FERGUSON, GEORGE PATTERSON. 

